Half-cell potential measurements cover the estimation of the electrical half-cell potential/corrosion potential of uncoated reinforcing steel in field and laboratory concrete, for the purpose of determining the corrosion activity of the reinforcing steel. The measurements can be used:

1. For in-service evaluation and for use in research and development work.
2. In members regardless of their size or the depth of concrete cover over the reinforcing steel.
3. May be used at any time during the life of a structure and in any kind of climate provided the temperature is higher than +2 °C

The corrosion potential Ecorr (half-cell rebar/concrete) is measured as potential difference (or voltage) against a reference electrode (half-cell). The numerical value of the measured potential difference between the steel in concrete and the reference electrode will depend on the type of reference electrode used and on the corrosion condition of the steel in concrete.

Depending on the spatial distribution of anodic and cathodic reactions on the surface of the steel and the conductivity of the medium, following two different types of corrosion can take place:

a) Uniform corrosion, in which anodic and cathodic reactions are coupled to form numerous micro-cells on the steel surface and occur on the same areas.

b) Macro-cell corrosion or localized corrosion, in which the anodic and cathodic areas of the corrosion process are separated in space with significant potential drop.